The present invention generally relates to received signal processing, and particularly relates to allocating receiver resources based on the allocation of downlink and uplink resources in the time domain.
Advanced wireless communication networks such as those compatible with the Third Generation Partnership Project (3GPP) employ complex signal transmission schemes. For example, Release 8 of the Universal Mobile Telecommunications System (UMTS) is presently under development by the 3GPP Long Term Evolution (LTE) project. The proposed air interface described in Release 8 of the UMTS standard uses Orthogonal Frequency Division Multiple Access (OFDMA) for downlink transmissions (transmitter to receiver) and Single Carrier FDMA (SC-FDMA) for uplink transmissions (receiver to transmitter). Other wireless communication standards employ similar downlink and uplink transmission schemes.
Advanced downlink and uplink transmission schemes typically involve both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) communication, where downlink and uplink sub-bands are separated by both a frequency offset (FDD) and a time offset (TDD). For example, with OFDMA, transmissions are divided in the time domain into time slots of duration 0.5 ms and subframes of duration 1.0 ms. Each frame is 10 ms long, and thus includes 10 subframes. Each subframe includes one or more blocks of data.
Receivers demodulate data blocks included in received downlink subframes. Receivers also report feedback information derived from the processed data to the transmitter by including the feedback information in available uplink subframes. The feedback information indicates how the receiver views the quality of the wireless communication environment. For example, a receiver conventionally reports whether blocks within a particular downlink subframe were successfully received and demodulated. Demodulation results are reported in the form of ACK/NACK reports (acknowledged/not acknowledged) which indicate whether subframes were successfully demodulated. Channel quality information may also be sent to the transmitter, e.g., in the form of a channel quality indicator (CQI) value. Other types of feedback information associated with downlink subframes may also be reported such as transmit power control information.
The transmitting device uses the feedback information to adjust the allocation of radio resources throughout the network. For example, a radio base station may allocate additional radio resources to receivers reporting a high signal quality environment, e.g., by providing a higher-order modulation scheme, increased data rate, etc. Conversely, less radio resources are allocated to receivers located in low quality environments in order to maintain an acceptable bit or symbol error rate.
Receivers are typically instructed when to report feedback information relating to downlink transmissions, e.g., N subframes after the current downlink subframe. However, the transmission configuration scheme may change within a network or between different networks. The transmission configuration scheme determines how subframes are allocated within a frame between downlink and uplink transmissions, i.e., the number of downlink and uplink subframes and when they are expected in time. For example, five downlink and five uplink subframes may be allocated for each frame. Alternatively, six downlink and four uplink subframes may be allocated per frame. Other combinations are also possible (e.g., 7/3 and 8/2). Typically, an uplink subframe must be available to report downlink feedback information.
Availability of uplink subframes depends on the current transmission configuration scheme. Fewer available uplink subframes causes a greater delay in feedback reporting when transmitting information using the TDD mode because all transmissions occur on the same carrier, i.e., uplink and downlink transmissions share the same carrier. For example, in half-duplex FDD transmission mode, an increased feedback reporting delay can occur when the user equipment cannot transmit and receive at the same time. The later an uplink subframe is available in time for reporting feedback information, the more time available for processing the corresponding downlink subframe because the feedback information generated from the downlink subframe need not be ready until just before the next uplink subframe is available. However, receivers are conventionally allocated the same fixed amount of time for processing received data blocks regardless of uplink subframe allocation. This limits receiver performance in networks where multiple transmission configuration schemes are used. Conventional receivers optimally process received data blocks for only a single transmission configuration scheme. If the density of uplink subframes changes, the receiver no longer processes received data blocks in the most efficient manner.